Weaning from mechanical ventilator is an essential element in the care of critically ill intubated patients receiving mechanical ventilation. It covers the entire process of liberating the patient from mechanical support and from endotracheal tube1. The process of weaning involves two-step strategies: 1. Assessment of readiness for weaning, including physiological measurement, such as maximum inspiratory pressure, tidal volume, respiratory rate and etc. 2. Spontaneous breathing trial. The incidence of successful weaning is estimated around 68.8%.